Mini Pre-amps--sound Professionals Or Reactive?

[mee]

Two mini pre-amps that could be used for portable recording:

http://www.soundprofessionals.com/c.../item/SP-PREAMP

and

http://www.reactivesounds.com/spa2.php

About the same price. Some feature comparisons:

The SP pre-amp has the size advantage, important for portable, stealth

recording. Both small and pocketable, but the Reactive PA is more than an

inch longer than the SP. (Other dimensions similar, Reactive even slightly

thinner. But significantly longer!)

But the Reactive PA ("Boost Box") looks like it has some other advantages.

Most notably, the clipping light. Since the H120 (mp3 player that records)

has no level meters, setting the gain and level on a pre-amp is normally

just guesswork, which I assume would occur with the SP PA. With the Reactive

unit, though, the directions say that you set it to lowest gain, then slowly

turn up the gain until the clipping light starts to light, then back off a

little. Also--simpler controls on the Reactive PA. Besides on/off, just one

continuous rotary dial to control gain.

The SP PA, on the other hand, has a three position switch for gain (0db,

29db, and 50 db), and a rotary dial for "level". (Could someone please

explain the difference between "gain" and "level"? Sorry for the newbie

question.) (The 0 db setting gives no pre-amp function at all, I guess then

functioning like a battery box, the 50 db setting is probably too high for

most uses, so I would guess most users leave the gain setting to 29db, and

do fine setting with the rotary level dial.

The Reactive web site states that it is much better for the rotary

(continuous) dial to control "gain", as theirs does, rather than "level", as

the SP does. What do those reading who understand "gain" and "level" think

of that statement? True? In any case, it certainly looks simpler to

set--just one rotary dial to set, using the clipping light for guidance.

With the SP PA you have to set the three way gain switch, and the rotary

level dial, and if you have no level meter, those two settings have to be

guessed.

I guess I'm leaning towards the Reactive Sounds "Boost Box", although I like

the smaller size of the SP PA. However, I am not too knowledgeable about

this stuff, and perhaps one of you could understand more of the specs of

these two units than I can. If someone has actually tried both and could

compare them, that would be great!

Any comments on comparing those two mini battery pre-amps--Sound

Professionals and Reactive Sounds, would be well-appreciated.

[dex Otaku]

As I have used neither, I can't comment on their build quality or testify as to their sonic characteristics or usability.

I would say this though: [in agreement with Reactive Sounds]

I'll note first-off that this is my understanding of how these work. It has been years since I studied how op-amps work and I can't be absolutely certain that my thinking is correct here. Perhaps Gerry from Reactive or someone with more background in analogue circuit design can correct me if I'm wrong.

Gain is how much the preamp amplifies the incoming signal by. A gain control lets you control how much amplification is taking place. This can be considered true impedance-matching, if I'm not mistaken, because the matching is done at the amp's input, not its output.

A level control, on the other hand, allows you to attenuate the output of a fixed-gain preamp. By fixed-gain I mean that gain is set at a single level; even with preamp like the SP model with 3 selectable gains, the gain is basically fixed to those three levels only, with only one gain applied at any given time, so I would call it fixed-gain - especially considering the fact that the only fine control you have is an attenuator on its output.

With a variable-gain preamp, its own noisefloor is determined by how much gain you're applying. As you increase gain, you increase the preamp's audible noisefloor along with the incoming signal. If you have very low-noise, high-efficiency amp in there, the noise can potentially be lower across the board, at all times.

With a fixed-gain preamp, the preamp itself is always applying a specific amount of gain and creating a specific amount of noise. The level control at its output can only attenuate the signal coming out of it, so both the signal and the noise are varied. Also, the fact that gain is fixed at a specific level at any given time means that more power is likely to be consumed at all times [unless gain is zero] as the preamp is always doing the same amount of work, with its output potentially being "wasted" by attenuation.

In the end this doesn't really mean that either is inherently lower-noise than the other [since noise varies along with signal in both cases], though variable-gain I would say is simply a more "proper" way of designing a preamp. Variable-gain, I would say, is a far more efficient way of doing things.

The preamp in MD and HiMD recorders appears to be fixed-gain [with two setting, low and high sensitivity] with its output variably attenuated, just like the SP preamp.

Again, I'll state that this is my understanding, and I'm just as likely wrong about how things work as right. My personal feeling is that the Reactive preamp is likely the better design, for the reasons stated above. I would rather have variable input gain than variable output attenuation, myself.

The only thing I see as a potential con with the Reactive preamp is its coiled cable; I would rather have a simple output and choose a cable of appropriate length, myself.

Anyone, please correct me if I'm wrong.

[Reactive]

Hi Dex,

Your description of the fixed gain vs the variable gain is mostly correct. To recapitulate: The fixed gain pre-amp is not the best way to boost a mic signal. Too much noise from the gain setting. Let me see if I can give an example that I can understand (sorry too many Canada Day celebrations yesterday).

Recording example:

You have a fixed gain pre-amp and your in a setting that requires a gain boost of approx. 35db. With a fixed gain pre-amp your only option is to choose from 29db or 50db. Your stuck in the middle with too liitle amplification or too much. Most likely your going to choose the 50db setting. But how do you know? No clipping meter or VU meter to guide you?

If you choose the 50db setting and your clipping the output, yes you can adjust the level down with the rotary level meter, but as Dex say's it's not an efficient use of the amplifier circuit. Why run it at full throttle and then have to lower the output level? It makes no sense.

The fully adjustable gain found on the Reactivesounds Boost box (from zero to 36db) is a more efficient design, with the clipping meter you can nail that recording time and time again. We chose the cut off point at 36db because I felt the noise level beyond this point would be too high. As I mentioned in a previous post, "the noise level is present at all times, and you can only ever get it down to a managable level" Sure if you throw ton's of money at it you end up with a Mackie style pre-amp, very quiet, expensive, and not suited for portable use.

Thanks

Gerry

www.reactivesounds.com

As I have used neither, I can't comment on their build quality or testify as to their sonic characteristics or usability.

I would say this though: [in agreement with Reactive Sounds]

I'll note first-off that this is my understanding of how these work.  It has been years since I studied how op-amps work and I can't be absolutely certain that my thinking is correct here.  Perhaps Gerry from Reactive or someone with more background in analogue circuit design can correct me if I'm wrong.

Gain is how much the preamp amplifies the incoming signal by.  A gain control lets you control how much amplification is taking place.  This can be considered true impedance-matching, if I'm not mistaken, because the matching is done at the amp's input, not its output.

A level control, on the other hand, allows you to attenuate the output of a fixed-gain preamp.  By fixed-gain I mean that gain is set at a single level; even with preamp like the SP model with 3 selectable gains, the gain is basically fixed to those three levels only, with only one gain applied at any given time, so I would call it fixed-gain - especially considering the fact that the only fine control you have is an attenuator on its output. 

With a variable-gain preamp, its own noisefloor is determined by how much gain you're applying.  As you increase gain, you increase the preamp's audible noisefloor along with the incoming signal.  If you have very low-noise, high-efficiency amp in there, the noise can potentially be lower across the board, at all times. 

With a fixed-gain preamp, the preamp itself is always applying a specific amount of gain and creating a specific amount of noise.  The level control at its output can only attenuate the signal coming out of it, so both the signal and the noise are varied.  Also, the fact that gain is fixed at a specific level at any given time means that more power is likely to be consumed at all times [unless gain is zero] as the preamp is always doing the same amount of work, with its output potentially being "wasted" by attenuation. 

In the end this doesn't really mean that either is inherently lower-noise than the other [since noise varies along with signal in both cases], though variable-gain I would say is simply a more "proper" way of designing a preamp.  Variable-gain, I would say, is a far more efficient way of doing things.

The preamp in MD and HiMD recorders appears to be fixed-gain [with two setting, low and high sensitivity] with its output variably attenuated, just like the SP preamp. 

Again, I'll state that this is my understanding, and I'm just as likely wrong about how things work as right.  My personal feeling is that the Reactive preamp is likely the better design, for the reasons stated above.  I would rather have variable input gain than variable output attenuation, myself. 

The only thing I see as a potential con with the Reactive preamp is its coiled cable; I would rather have a simple output and choose a cable of appropriate length, myself.

Anyone, please correct me if I'm wrong.

←

[dex Otaku]

Thanks, Gerry.

[mee]

As I have used neither, I can't comment on their build quality or testify as to their sonic characteristics or usability.

In looking at their published specifications (see URLs in OP), it looks like the SP PA has a higher S/N ratio than the Reactive PA. I think a couple of other specs (frequency, etc.) looked better on the SP spec list.

I don't know how accurate the specs are, however, and whether they would make an audible difference. Anyone know?

[dex Otaku]

In looking at their published specifications (see URLs in OP), it looks like the SP PA has a higher S/N ratio than the Reactive PA. I think a couple of other specs (frequency, etc.) looked better on the SP spec list.

←

I take a company's specs with a block, not a grain, of salt. Until I have one in my hands and can measure its performance in comparison to my other equipment, listed specs are only a reference point, and can never be fully trusted.

That said, I do quote them, but I usually point out that I don't own what I'm quoting specs about.